The present invention relates generally to electrical control devices and more specifically to an electromechanical actuator including a passive cooling system.
There is a growing trend in the design of modern aircraft control systems to replace the well known control surface hydraulic actuators with localized, dedicated electromechanical actuating devices. The overall aim is to eliminate the aircraft hydraulic system in order to enhance simplicity, reduce operating costs, reduce aircraft weight and avoid loss of aircraft control situations due to hydraulic system failure. Military aircraft are perhaps especially vulnerable to hydraulic system failure from flight critical battle damage received during combat. Both military and civilian aircraft, however, would benefit from the elimination of the hydraulic control systems in favor of dedicated, individual electromechanical control devices.
As is well known, electromechanical actuators are inefficient during operation. The waste heat generation of the electromechanical actuators average 10-25% of their power, which must be removed in order to assure continuous, reliable operation. While hydraulic actuators also generate waste heat, this heat is removed by the central hydraulic system and discharged at a remote location. While it would be possible to provide a central cooling system to cool the electromechanical actuators, much of the benefit otherwise gained by the utilization of the individual electromechanical actuators would be lost because one centralized system is simply substituted for another. Moreover, the increased complexity of such a central cooling system including the attendant pumps, valves, plumbing, etc. serves to eliminate this as a choice of a viable, alternative system.
One recent approach to providing a self cooling electromechanical device is found in U.S. Pat. No. 5,770,903 to Bland et al. disclosing a reflux-cooled electromechanical device including a housing surrounding the stator defining a sealed boiling chamber. The boiling chamber contains a fluid for transferring heat and a condenser for removing the heat externally from the boiling chamber. While this device does provide a degree of heat transfer from the electromechanical actuator, a need for improvement exists. More specifically, because of the boiling chamber design, the heat transfer characteristics of this device change dramatically with changes in G loading forces as would be encountered by modern military aircraft in flight.
A need exists therefore for an improved self cooled electromechanical actuator Such a device would be capable of providing independent, reliable operation in a range of operating conditions from &lt;&lt;1 G to 10 G.